"Expand" working only with fields named the same as collection

[zzzaaa]

For example I have two collection: Contact(id, name) and Post(id, createdBy)
Post.createdBy is linked to Collection

I try to execute:

$proxy->PostCollection()-> Expand('createdBy')->Execute();

It's throw error
Property Post::$Contact does not exist

AtomParser.php

 $property = new ReflectionProperty($object, $entryType);

$object contain Post object.
$entryType is string 'Contact'